There are a number of challenges in developing drugs for therapeutic use in a patient population. Many initial agents do not reach the market for any number of reasons (e.g., lack of clinical benefit or lack of proven safety in a patient population). Some critical issues for the development of effective and safe drugs are: (1) establishing that a drug interacts with its intended molecular target in a patient population; (2) establishing that the specific target is relevant to treating the particular disease in the same patient population; and (3) identifying a biologically optimal dose based on the drug's effect on the target in the same patient population. The development of an appropriate companion diagnostic for a particular drug helps significantly in developing a drug for use in a clinical patient population.
A companion diagnostic coupled with molecular imaging provides a powerful, non-invasive 4-dimensional assessment of a molecular target and its interaction with drug molecules in vivo. Some examples of imaging platforms includes: magnetic resonance imaging (MRI); positron emission tomography (PET); single photon emission tomography (SPECT); optical imaging, computed tomography (CT); ultrasound, X-ray or photoacoustic imaging. Selection of an imaging contrast takes into account the specific molecular probe and intrinsic tissue characteristics. The coupling of a companion diagnostic with molecular imaging allows for a better understanding of a particular drug's interaction with its molecular target in patients, which can help in identifying potential responders to the specific drug and aid in the understanding and determination of the mechanisms of sensitivity and resistance of the drug (and its optimal dosing).